Mechanical hyperalgesia and inflammation induced by formalin in rats

In an attempt to evaluate the time-dependent analgesic and anti-inflammatory effects, OP₅ and OP₆ were tested acutely in formalin-induced pain. The effect of 10 days repeated administration of OP₅ (2.5 and 5 mg/kg/day as a single bolus) was also tested. NaCl 0.9 % and diclofenac were respectively used for negative and positive controls. One hour after oral administration of various substances, pain and inflammation were induced by injecting 0.1 ml of a 2 % formalin solution, under the left hind paw of each rat [17]. Ugo Basile analgesy meter no. 372157 and the caliper were used to measure the response threshold of each animal to mechanical pain and the paw diameter, respectively. The response threshold of the animal to mechanical pain was reported before treatment and 1, 2, 4, 6, 8 and 24 h post injection for the first day and once a day for ten days. The diameter of the injected paw was measured before treatment and 3, 5, 7 and 24 h post injection for the first day and then once a day for ten days. For repeated treatments, drugs were administered once a day, after collection of data. At the end of the experiment, the antioxidant, hepatotoxic and ulcerogenic effects of chronic administration of OP₅ were examined. On this purpose, animals were sacrificed on day 11. Blood, kidney and liver samples were collected. Serum was separated for ALAT and ASAT assays. Kidney and liver were homogenized in Tris buffer and centrifuged. The supernatant was used to assay nitric oxide, malondialdehyde, superoxide dismutase, catalase and glutathione. Immediately after blood, liver and kidney collection, the stomach was carefully dissected out and opens along the great curvature. The mucus weight and ulceration index were estimated as previously described [18].